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Abstract - The paper contains analysis of possibilities for realization a large radius circular motion suitable for a portable measurement system for bidirectional texture functions (BTF) measurement. This circular motion will be used for changing the position of an array of detection cameras taking snapshots of sample illuminated by LED modules. The constrains for the proposed circular motion design are: large radius of motion about 300 mm limited to angular motion about 12°, non-accessibility of the centre of rotation which has to be kept free, total mass and price of the solution and motion deviation from centre point. We present three possible solutions comprising a single stiff curved guide with a ball roller, a curved guide with fixed rollers and two separated linear guides. We include an additional factor - the angular deviation of concentrically arranged array of cameras to - evaluate the optimal solution reaching BTF measurement instrument needs.
Keywords: Bidirectional texture functions (BTF), portable instrument, measurement, circular motion.
1. Introduction
Bidirectional texture functions (BTF) measurement is one of the most important techniques in computer graphics how to process real appearance of surface textures. This technique is based on taking and analyzing a surface reflectance from a large number of snapshots taken under different combination of observer and illumination directions. Successful data processing necessary for high rendering quality needs thousands of surface images taken with high image resolution. Such process is time consuming and typically performed using stationary gantries [1, 2, 3] because of presence of expensive high resolution cameras, control systems and broad and precise mechanical motions. Such instruments are limited to measuring small samples or their fragments, but it is not possible to acquire data of large fixed samples or specimens which may change its pattern in time or when removed. There were developed few portable systems, which try to tackle such problems [4, 5, 6]. We recently successfully developed portable BTF measurement system based on single high resolution camera and kaleidoscopic imaging using multiple reflections within six mirror's kaleidoscope [7, 8, 9]. Our next goal is to develop another system based on multiple low resolution cameras and to compare both data acquisition approaches. We want to cover all possible combinations of camera directions and illumination directions to eliminate data...